Floating point rounding modes: we should restrict them slightly

[Walter Bright]

Don wrote:
> Walter Bright wrote:
>> bearophile wrote:
>>> An important purpose of a not bug-prone language is remove as many
>>> undefined situations as possible.
>>
>> That's right.
>>
>>> If you add that to D2 specs, can
>>> the compiler catch at compile time all cases of violations to that
>>> rule?
>>
>> Unlikely. But that has to be weighed against the former behavior being 
>> defined in a useless way.
> 
> We could get close, I think. We could catch all violations in SafeD. 
> Disallow calling core.stdc.fenv functions from inside SafeD modules, and 
> provide an RAII object in std.math for changing the rounding mode.
> 
> Actually there's probably a few other C functions we want to prohibit in 
> SafeD -- the infamous string functions, for example.

Yes, all the C functions will have to be gone through and separated. 
strlen() is safe, while strcpy() and printf() are not.


> I think the goal should be try to remove undefined behaviour from SafeD.
> Long term goal: "If a program uses no system modules other than those 
> provided in the standard library, it should not be exposed to undefined 
> behaviour." ?

Right!